Method and system for preconditioning an emission control device for operation about stoichiometry
First Claim
1. A method for controlling the operation of an internal combustion engine, wherein the engine operates at a plurality of operating conditions characterized by combustion of a range of air-fuel mixtures to generate exhaust gas, the exhaust gas flowing through an emission control device, the method comprising:
- selecting a first engine operating condition, characterized by combustion of a first air-fuel mixture having a first air-fuel ratio lean of a stoichiometric air-fuel ratio, for a first time period sufficient to store a substantial amount of oxygen and an exhaust gas constituent in both an upstream portion of the device and a downstream portion of the device;
selecting a second engine operating condition, characterized by combustion of a second air-fuel mixture to the engine having a second air-fuel ratio rich of the stoichiometric air-fuel ratio, for a second time period sufficient to release a substantial amount of the stored oxygen and stored exhaust gas constituent from only the upstream portion of the device; and
selecting a third engine operating condition for a third time period, the third engine operating condition being characterized by combustion of a third air-fuel mixture having a time-varying range of air-fuel mixtures including air-fuel ratios that are both lean and rich of the stoichiometric air-fuel ratio, the third operating condition being further characterized by exhaust gas lacking an amount of excess hydrocarbons sufficient to purge substantially all oxygen and exhaust gas constituent stored in the downstream portion of the device during the first engine operating condition, and lacking an amount of excess oxygen sufficient to substantially fill the upstream portion of the device with oxygen and the exhaust gas constituent.
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Accused Products
Abstract
An exhaust gas treatment system for an internal combustion engine includes a three-way catalyst and a NOx device located downstream of the three-way catalyst. The device is preconditioned for emissions reduction at engine operating conditions about stoichiometry by substantially filling the device with oxygen and NOx; and purging stored oxygen and stored NOx from only an upstream portion of the device, whereupon the upstream portion of the device operates to store oxygen and NOx during subsequent lean transients while the downstream portion of the device operates to reduce excess HC and CO during subsequent rich transients.
153 Citations
7 Claims
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1. A method for controlling the operation of an internal combustion engine, wherein the engine operates at a plurality of operating conditions characterized by combustion of a range of air-fuel mixtures to generate exhaust gas, the exhaust gas flowing through an emission control device, the method comprising:
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selecting a first engine operating condition, characterized by combustion of a first air-fuel mixture having a first air-fuel ratio lean of a stoichiometric air-fuel ratio, for a first time period sufficient to store a substantial amount of oxygen and an exhaust gas constituent in both an upstream portion of the device and a downstream portion of the device;
selecting a second engine operating condition, characterized by combustion of a second air-fuel mixture to the engine having a second air-fuel ratio rich of the stoichiometric air-fuel ratio, for a second time period sufficient to release a substantial amount of the stored oxygen and stored exhaust gas constituent from only the upstream portion of the device; and
selecting a third engine operating condition for a third time period, the third engine operating condition being characterized by combustion of a third air-fuel mixture having a time-varying range of air-fuel mixtures including air-fuel ratios that are both lean and rich of the stoichiometric air-fuel ratio, the third operating condition being further characterized by exhaust gas lacking an amount of excess hydrocarbons sufficient to purge substantially all oxygen and exhaust gas constituent stored in the downstream portion of the device during the first engine operating condition, and lacking an amount of excess oxygen sufficient to substantially fill the upstream portion of the device with oxygen and the exhaust gas constituent. - View Dependent Claims (2, 3, 4)
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5. A system for controlling the operation of an internal combustion engine, wherein the engine operates at a plurality of operating conditions characterized by combustion of a range of air-fuel mixtures to generate exhaust gas, the exhaust gas flowing through a three-way catalyst and a lean NOx device, the system comprising:
a controller including a microprocessor arranged to select a first operating condition characterized by combustion of a first air-fuel mixture to the engine having a first air-fuel ratio lean of a stoichiometric air-fuel ratio for a first time period sufficient to store a substantial amount of oxygen and NOx in both an upstream portion of the device and a downstream portion of the device, and to select a second operating condition, characterized by combustion of a second air-fuel mixture to the engine having a second air-fuel ratio rich of the stoichiometric air-fuel ratio for a second time period sufficient to release a substantial amount of the stored oxygen and stored NOx from only the upstream portion of the device, and wherein the controller is further arranged to select a third operating condition for a third time period, the third operating condition being characterized by combustion of a third air-fuel mixture having a time-varying range of air-fuel mixtures including air-fuel ratios that are both lean and rich of the stoichiometric air-fuel ratio, the third operating condition being further characterized by exhaust gas lacking an amount of excess hydrocarbons sufficient to purge substantially all oxygen and NOx stored in the downstream portion of the device during the first operating condition, and lacking an amount of excess oxygen sufficient to substantially fill the upstream portion of the device with oxygen and NOx. - View Dependent Claims (6, 7)
Specification